<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="./js/react.development.js"></script>
  <script src="./js/react-dom.development.js"></script>
  <script src="./js/babel.min.js"></script>
</head>
<body>
  <div id="app"></div>



  <script type="text/babel">

    const courses = [
      {id: 1, name: 'React'},
      {id: 3, name: 'Vue'},
      {id: 5, name: '小程序'},
      {id: 6, name: 'xxx'}
    ]
    
    // 根据数据的数组生成标签的数组
    const lis = courses.map(course => <li key={course.id}>{course.name}</li>)

    const vDom = (
      <div>
        <h2>前端框架列表</h2>  
        <ul>
          {
            // [
            //   <li key={courses[0].id}>{courses[0].name}</li>,
            //   <li key={courses[1].id}>{courses[1].name}</li>,
            //   <li key={courses[2].id}>{courses[2].name}</li>,
            //   <li key={courses[3].id}>{courses[3].name}</li>
            // ]

            // 根据数据的数组生成标签的数组
            // courses.map(course => <li key={course.id}>{course.name}</li>)

            lis
          }
        </ul>
      </div>
    )

    /* 
    错误: Warning: Each child in a list should have a unique "key" prop

    React要求列表中的每个元素都需要有个唯一的key值 ==> 内部优化
    key值尽量用id值, 不要用下标  => 后面会讲
    */
   

    // 渲染虚拟DOM
    ReactDOM.render(vDom, document.getElementById('app'))
  </script>
</body>
</html>